1. Field of the Invention
This invention involves a process for coating a metal surface to produce increased resistance to penetration, abrasion and corrosion. The process comprises the electroless deposition of nickel, the ion beam deposition of silicon, and the deposition of a diamond-like carbon (DLC) coating.
2. Description of the Prior Art
Metal surfaces have long been coated in order to protect such surfaces from wear, abrasion, and corrosion. Chromium has been used in the prior art as a coating for metal surfaces. Prior art methods have employed the electrodeposition of hard chromium from a chromate bath to coat metal surfaces. The resulting chromium coating has a hardness greater than that of tool steels and further has a very high resistance to both general and pitting corrosion. Such corrosion frequently occurs in a marine or chloride-containing environment.
Chromium coatings applied by electrodeposition have also been used to refurbish or restore a worn metal surface to its original dimensions. The use of chromium for refurbishment has involved stripping the residual chromium coating from the worn workpiece, applying a layer of hard chromium by electrodeposition and machining the workpiece to provide a wear-resistant surface within the desired dimensional tolerances.
Although the use of hard chromium has been satisfactory in terms of protecting the underlying metal surface, the use of hexavalent chromium electrolyte, required for electrodeposition, is environmentally undesirable. Hexavalent chromium electrolyte is toxic. Environmental regulations enacted by the United States Environmental Protection Agency (EPA) severely restrict the use of toxic hexavalent chromium electrolyte for use as a restorative coating.
No prior art method has been devised to provide a coating for a metallic surface with the wear resistant and corrosion resistant characteristics of a hard chromium coating, without the adverse environmental effects resulting from the electrodeposition of hard chromium.